A navigation device may use information from a dead reckoning navigation system to estimate its current position. A dead reckoning navigation system may include a compass, a plurality of optional accelerometers, and a plurality of optional gyroscopes, to estimate position. The compass senses direction. The accelerometers sense linear acceleration of the navigation device platform. The gyroscopes sense rotation of the navigation device platform. Changes in position are determinable from the sensed linear acceleration, in view of the sensed direction, of the navigation device platform.
The navigation device may also use information from a global navigation satellite system (GNSS) to estimate its current position. Examples of GNSS systems include, but are not limited to, global positioning systems (GPS) or long range navigation systems (LORAN).
When the GNSS device receives a sufficient number of satellite signals so as to accurately determine location, the navigation device may substantially rely on the location information provided by the GNSS device. However, if the GNSS device is unable to accurately determine its location, such as when an insufficient number of satellite signals are available, the inaccurate location information from the GNSS device may result in an undesirable error in the navigation device's estimated location.
GNSS devices are often unable to accurately determine location when in a structure, such as a building or parking garage. For example, satellite signals may be lost such that the GNSS device is unable to determine location. As another example, satellite signal reflections may be detectable by the GNSS device. However, such satellite signal reflections may introduce errors in the location information determined by the GNSS device.
In the event that the navigation system determines that the location information provided by the GNSS device is in error, the navigation system will then rely on its dead reckoning navigation system to estimate its position. However, until the navigation device recognizes that the location information provided by it GNSS device is no longer valid, the navigation device will incorrectly estimate location since it is relying on the invalid location information provided by its GNSS device.
Accordingly, there is a need to more quickly and reliably detect the occurrence of invalid location information provided by the GNSS device. The need to more quickly and reliably detect the occurrence of invalid GNSS location information is even more important in navigation devices that can be expected to be taken into a structure since the structure is likely to disrupt the ability of the GNSS device to receive a sufficient number of satellite signals which are used to determine the GNSS location information.